Printing blanket and method of making the same



Dec. 31, 1968 w. C. Ross 3,418,864

PRNTING BLANKET AND METHOD 0F MAKING THE SAME Filed Jan. .'51, 1964FIG.|

United States Patent C) 3,418,864 PRINTING BLANKET AND METHOD F MAKINGTHE SAME William Campbell Ross, Winchester, Mass., assignor to W. R.Grace & Co., Cambridge, Mass., a corporation of ConnecticutContinuation-impart of application Ser. No. 280,872, May 16, 1963. Thisapplication Jan. 31, 1964, Ser. No. 341,547

9 Claims. (Cl. 74-232) ABSTRACT 0F THE DISCLOSURE This is acontinuation-in-part of application Ser. No. 280,872, filed May 16,1963, now abandoned.

This invention relates to printing blankets and especially to -blanketsadapted for use on screen print machines.

Printing blankets used on screen print machinery are very large, and areenormously heavy. Frequently they are some 100 inches wide, and 100yards long. Such blankets are formed in a closed loop. The materialwhich is to be screen printed is glued to the blanket, and as each colorstep is imprinted on the goods, the blanket is advanced through onerepeat pattern. As a consequence, the entire -blanket must start, move,and stop with an extraordinary degree of exactitude. lf the variation inan entire traverse of the loop at any point exceeds 40 thousandths(0.040) of an inch, interior printing will occur. If the amount ofstretch as the blanket advances through one repeat pattern is greaterthan or less than the stretch in the preceding step, the pattern willnot lit This is serious, for t in the textile printing sense means thateach color, as it is successively applied, has been placed in the exactposition required by the design. When t is poor, some color marginsoverlap, the printed design on the finished goods appears mushy, andsometimes unpleasant color mixing results. Poor fit results in severeeconomic loss, for the printed goods can then only be sold at sacrificeprices.

So far as I am aware, no blanket presently maintains a suiciently highdegree of dimensional stability. Consequently, in screen printingmachinery, various mechanical expedients have been used to stop eachindividual repeat of the blanket as exactly the right position under thevarious colored screens. Nonetheless, variable stretching still remainsa problem despite these expedients, and whenever the blanket stretcheso-r recovers from stretch in a non-uniform manner as it advances aroundthe loop, poor fit results.

The present invention produces a blanket in which movement of theworking surface is inconsiderable and makes it possible to operate ascreen printing machine with blanket lengths of 100 yards withoutmechanical correcting devices. The operating speed can be 800 yards perhour or more, yet at this speed the blanket maintains the necessarytolerance of no greater than 15 thousandths (0.015) of an inch at anypoint in the whole blanket run.

The process of screen printing is essentially a stencil operation and sodiffers materially `from the engraved roller rotary textile printingprocess. Screen print blankets do not have to withstand the enormouscompressional load which, in roller printing, is imposed by the colorrolls. Their working surfaces do not have to withstand the compressionalwave which travels along the blanket, and, in contrast to a roller presstextile print blanket, they do not have to transmit any significantamount of power, for in roller type textile printing, much of theauxiliary 3,418,864 Patented Dec. 31, 1968 equipment, particularly theblanket washer, is driven by the blanket itself. In short, the onlydemands on a screen printing blanket are that it shall remain tight, at,have substantially no tracking error, and be strong enough to moveitself, without variable stretch.

In view of the very successful constructions of textile print -blanketsused in engraved roller printing and the phenomenal service life whichthey deliver under vastly more drastic conditions, it `would be expectedthat blankets made in the manner found satisfactory for this type oftextile printing could be used on screen printing machinery.Su-rprisingly, this is not the case.

Although these blankets give absolutely clean, sharp, and brilliantpatterns on textile printing presses, the color outlines do not fitaccurately when such blankets are used on screen printing machinery.Careful measurements have disclosed that in screen printing service,such blankets change lengths minutely as the blanket progresses throughsuccessive repeat pattern steps.

A construction which is common in power transmission belts was thentried. A continuous, longitudinal winding of cord located in essentiallythe median plane of the blanket was tried. But although cords in such aposition are placed where the compressional and extension forces actingon the cords as the blanket passes over the pulleys are both at minimumvalues, and where the cords as the limiting members should control thelength of the blanket, such blankets were unsatisfactory. They exhibiteddimensional change greater than that which good screen printing permits.

After considerable experimentation, it was determined that the criticalplane where dimension control must be exerted on a screen print blanketwas neither the median plane nor the working surface but a plane whichlay as near as possible to the plane of the cylinder ply. This nding isall the more remarkable when it is remembered that the cloth in screenprinting is cemented to a working surface which is remote from thecords, and that it is the movement of the cloth together with themovement of that working surface which destroys the sharpness andclarity of the print.

Nonetheless, it Iwas found that the critical position where lineardisplacement must be prevented is at and adjacent to the surface whichis in contact with the drive roll. In printing machines, the blanket iseither pushed or pulled as it moves ahead, step by step.

The general solution to this problem was achieved by adopting theconstruction which is illustrated in FIGURE 2, and assembling theblanket in the manner which follows.

A base ply of duck is coated on one side with a vulcanizable rubbercompound. This forms the base or cylinder ply of the blanket. Twopulleys are arranged so that the cylinder ply, when stretched over them,forms a loop. The ends of the fabric are then spliced together.Subsequently power is applied to `one of the pulley shafts and the plyis tensioned in small successive increments until the tension of thefabric is about 10- pounds per transverse inch. The running-in of theply is continued under tension until no slack develops and the plymaintains an exact length. The time of run-in is variable, depending onthe tightness of weave of the canvas. Thereafter, an essentiallynon-stretchable cord which previously has been coated with a rubbercompound is laid on the rubber-covered surface of the cylinder ply withtension maintained on the ply. A continuous length of this cord ishelically wound from the center to the margin. To eliminate pucker orstretch, two windings are simultaneously wound from the centeroutwards-one extending to the left and the other extending to the righthand margins of the ply. The tension of the cylinder ply with attachedcords is then increased to generally between about 20 to 40 pounds andpreferably about 25 pounds. Thereafter a ply of duck, coated on bothsides with a vulcanizable rubber compound is laid over the cords and isspliced at a point remote 4from the splice in the cylinder ply. Afurther (third) ply of duck, coated with a vulcanizable rubber compoundis then laid on the cordcovering layer and is spliced at a point remotefrom the two underlying splices. Ordinarily, the top surface of thisthird ply is coated with a heavy coat of a solventresistant rubbercompound which, when press-curing is complete, forms the working surfaceof the blanket. The entire assembly or sandwich is then press-curedunder quite heavy pressures in a heated vulcanizing press. As theblanket cures and the rubber flows, the cords become totally embedded inrubber compound. The covering plies of duck are entirely embedded andthe top or working surface of the blanket becomes a smooth, unbrokenrubber sheet.

Occasionally, when certain proprietary cloth cements or glue are to beused, it is desired that fabric shall be exposed on the top workingsurface. Accordingly, the top rubber coating can be omitted.

The run-in of the coated cylinder ply under tension and before theassembly of the blanket is commenced appears to be a necessary step. Ifthat step is omitted, minor dimensional changes in the blanket willoccur. lt also appears to be necessary to maintain the pull or tensionunder which the cords are wound on the cylinder ply at some unchangingvalue, which should be uniform throughout the entire winding operation.However, the tensioning of the cords should be held to a minimum, andpreferably less than two pounds per cord.

Generally, to prevent the stretching of one margin of the blanket morethan the other, and to minimize any tracking error-in the resultingblanket, it is preferred that the cord winding, superposed on thecylinder ply, be two opposed helices starting from the center andrunning outwardly to each margin. There are certain canvas constructionswhich are so tight that stretching one margin more than the other as thecord is wound on the ply does not occur. If the cylinder ply is of suchcanvas construction, the cord may then be wound uninterruptedly from oneselvage to the other.

In the drawings:

FIG. l is a perspective view of a portion of the blanket 10.

FIG. 2 is an exploded sectional view.

Referring to FIG. 2, the cylinder ply, 12, carries a rubber coating, 13(which later forms part of the rubber embedment of the cords). Thehelices, 14, of rubbercoated cords are wound on top of rubber coating,13. The covering ply, 15, carries a rubber coating on each face. Thelower coating, 16, later forms the top half of the cord embedment. Theupper coating, 17, later unites with the lower coating, 18, of thecanvas ply, 19. The top surface of ply, 19, carries a rubber coating,21, which later becomes the working surface.

The number of plies is not critical. Another or even more intermediateplies may be added if required. Ply, 19, can be omitted, provided ply,15, is dense and very tightly woven. Usually, however, its presence isan advantage.

It is, of course, to be understood that after the blanket has beenexposed to vulcanizing heat and pressure in the vulcanizing press, therubber layers are indistinguishable and f-orm a solid rubber mass inwhich all of the fibrous elements, whether cords or fabric, areembedded. In the curing operation, the rubber flows. It thoroughlyinterpenetrates all of the space between the strands of the textile, andin many places penetrates deeply into the interber spaces of the textilestrands themselves. The cords are completely embedded in the rubberwhich has flowed around them. The surface of the blanket, which is curedagainst a polished sheet, is smooth and free of any Cil surfaceimperfection. The cords, save for the surrounding rubber, take up aposition which is immediately adjacent to the cylinder ply.

Example l A base ply of No. l2 duck was coated on one side withyapproximately "710 of a pound per square yard of vul-canizable neoprenerubber compound (Neoprene Type WRT, E. I. du Pont de Nemours & Co.,Inc., Wilmington, Del.). Two pulleys were then set up so that when thiscylinder ply was stretched over them, the loop which was formed was 40yards long. The fabric was then spliced. Subsequently, power was appliedto one of the pulley shafts, and the loop was tensioned in smallsuccessive increments until the tension of the fabric Was l0 pounds pertransverse inch. Run-in was continued until, under a tension of 10pounds per transverse inch, no slack developed, and the ply maintainedan exact length. Thereafter, two 6-ply, 2.70 denier cords of saponifiedacetate rayon (Fortisan), which previously had been coated with avulcanizable neoprene rubber cornpound (Neoprene Type WRT), were woundon the entire loop of the cylinder ply while the cylinder ply was stillunder tension. The cord winding was started at the ply center, and eachcord was run outwardly from the center to the selvage as a continuoushelix, one helix running in a right-hand direction, the other runninglefthanded. The pitch of the cord was such as to maintain a uniformspacing between the cords of 1/8 of an inch. During the entire winding,the tension applied to the cord was maintained at a uniform value.Thereafter, a ply of No. 12 duck, coated on its under side with 5%@ of apound per square yar-d of a vulcanizable neoprene compound (NeopreneType WRT) and having its upper side coated with i710 of a pound persquare yard of a second neoprene compound (Neoprene Latex Type 571, E.I. du Pont de Nemours & Co., Inc., Wilmington, Del.) was laid over thecords and spliced at a point remote from the splice in the cylinder ply.A third ply of duck, coated with 2/10 of a pound of neoprene compound(neoprene latex type 571) on its under side and having its top surfacecoated with sufficient butadiene-acrylonitrile rubber (Hycar 1051, highacrylonitrile, B. F. Goodrich Company, Cleveland, Ohio) to produce asurface 0.015 of an inch thick was laid over the cord covering layer andspliced at a position remote from the two underlying splices. The wholeblanket was then passed through a vulcanizing press, with a polishedmetal sheet interposed between the top platen and the top surface coatof rubber. The blanket was vulcanized at 310 F. under a 500 pounds persquare inch pressure.

Example Il A smaller test blanket was constructed in the same manner asthat used for construction 'of the blanket of Example I. Samples oneinch wide by 18 inches long, some of which contained a fabric splice andothers containing no splice, were placed in a tensile test apparatus, soarranged that the tension load could be varied at a given instant andthus simulate the load change in stopping and in starting a screen printmachine. The deviations in stretch were carefully measured in a seriesof such pulls exerted on eaoh of the samples. At equilibrium conditions,both the spliced and the unspliced sections of the blanket of Example IIshowed essentially no deviation in stretch.

As a counter-example, samples one inch wide and 18 inches long were lcutfrom a blanket now commercially employed. These samples were tested inthe same machine and in the same manner. In the commercial blanket, thedeviation in extension of the spliced sample, when compared to thedeviation in extension of an unspliced sample when undergoing a load of10 pounds per inch width to pounds per inch Width, was 0.025 in. (25mils). In going from 50 pounds per inch Width to 100 pounds per inchwidth, an additional deviation in extension of 0.017 in. (17 mils)occurred.

The large blanket of Example I was placed on an Ichinose automaticscreen printing machine. Extremely diflicult patterns were selected froma number which previous experience had shown could not be run on themachine because of mis-registration. Various repeat lengths and speedswere evaluated in printing runs which totaled 100,000 yards. No repeatpattern deviation was found in any run which varied from theabove-mentioned i0.015 in limits.

In contrast, when similar runs were made on the same textile materialcarried on a commercial blanket on the same machine, deviations inregister of 3h@ of an inch resulted.

Particularly useful as cords in the present invention are glass cords.The low stretch of the glass cord permits the construction of a blankethaving less loverall stretch and 100 percent elastic recovery and,therefore, greater repea accuracy than blankets with, for example, rayoncords. Since glass cords have more strength per unit diameter than othersubstantially nonstretchable cords, glass cords of smaller diameter canbe used which exhibit considerably less tendency to show through thesurface of the top ply of the finished blanket after curing and whichstill will provide the necessary strength and dimensional control.

Since the glass cords laid on the cemented cylinder ply may crimp inpassing around the circumference of the end rolls during theconstruction of the blanket, it may be desirable to apply a greaterdegree of tensioning to the carcass during the assembly of the blanketand during the cure than is applied to a blanket of nonglass cords. Thedegree of tension maintained during the application of the top plys andthe cure is a variable depending upon the diameter of the cord and thediameter of the end roll. In a preferred embodiment 20 to 40 pounds pertransverse inch is applied and more preferably, about 25 pounds.

Example III A base ply of No. 12 duck was coated on one side withapproximately A0 of a pound per square yard of vulcanizablebutadiene-acrylonitrile rubber compound (Hycar 1051, high acrylonitrile,B. F. Goodrich Company, Cleveland, Ohio). Two pulleys approximatelyinches in diameter were then set up so that when this cylinder ply wasstretched over them, the loop which was formed was 24 yards long. Thefabric was then spliced. Subsequently power was applied to one of thepulley shafts, and the loop was tensioned in small successive incrementsuntil the tension on the fabric was 10 pounds per transverse inch.Run-in was continued until, under a tension of 10 pounds per transverseinch, no slack developed and the ply maintained an exact length.

Thereafter, with tension maintained on the ply, two 3-ply glass yarns(Owens-Corning-E.C.G. 1501/3) which previously had been coated with avulcanizable butadiene-acylonitrile rubber compound (Hycar 1051) havling20 percent solids and a coating pickup of 2.67 wet pounds per thousandyards of cord were wound on the entire loop of the cylinder ply. Thecord winding was started at the ply center, and each cord was runoutwardly from the center to the selvage as a continuous helix` onehelix running in a right-hand direction and the other runningleft-handed. The pitch of the cords was such as to maintain auniform layof 12 cords per transverse inch. Each of the cords was maintained undera tension during the Winding of approximately 1 pound, and this tensionwas maintained at a uniform value throughout the entire windingoperation. The wound loop, or carcass, was then removed from the windingframe and taken to a lay-up and vulcanizing assembly station. Two rollsapproximately 10 inches in diameter were arranged in a similar set-up tothose used in the run-in and cord-winding operation. In this case,however, the rolls were so arranged in front and behind the vulcanizingpress that the loop passed through the press. The axle of one of therolls was then jacked backwards until the tension applied to the carcassbetween the lrolls was 25 pounds per transverse inch. A ply of No. 12duck coated on its under side with V10 of a pound per square yard of avulcanizable butadiene-acrylonitrile rubber compound (Hycar 1051) andhaving its upper side coated with 2/10 lbs. per square yard of a secondbutadiene-acrylonitrile rubber compound (Hycar 1042, med-highacrylonitrile, B. F. Goodrich Company, Cleveland, Ohio) was laid overthe cords and spliced at a point remote from the splice in the cylinderply. A third ply of duck, coated with 2A@ of a pound ofbutadiene-acrylonitrile rubber compound (Hycar 1042) on its under side,and having its top surface coated with sufficientbutadiene-acrylonitrile rubber compound (Hycar 1051) to produce asurface of 0.015 of an inch thick, was laid over the intermediate plyand spliced at a position remote from the two underlying splices.Maintaining the tension of 25 pounds per transverse inch, the wholeblanket was then passed through the vulcanizing press which had apolished stainless steel sheet interposed between the top platen and thetop surface coat of rubber and the bottom platen and the bottom surfacecoat of rubber. The blanket was vulcanized at 310 F. under a pressure of500 pounds per square inch. This blanket, when completed, was installedon a Stork Automatic Screen Printing machine and tested for accuracy inrepeat steps in the following manner:

After the blanket was properly installed and tensioned, a coating ofcolor was applied to the blanket surface and a hairline was drawntransverse to the blanket at the far end. The blanket was then rotateduntil the hairline appeared at the head end of the machine, and amatching hairline index attached to a xed portion `of the machine wasset in position. Thereafter, the blanket was run through a successi-onof step-and-repeat operations, hairlines being drawn on the blanket atthe head end of each repeat. Deviation between each repeat and the xedindex marks was read as the blanket progressed through several entirestep-and-repeat cycles. In no instance did the deviation exceed i0.015in. per blanket revolution.

The use of the blanket of this invention on screen printing machines,particularly those which use a simple endroll drive such as the Ichinoseand the Stork machines, eliminates the need of mechanical stops, steelbelt reinforcements, or other more complicated beltadvancing equipment.The only mechanical stop equipment required is that used to control themovement of the drive roll. On such machines using only `roll stopcontrol, color registration is remarkably Well sustained from repeat torepeat throughout the Whole piece of goods.

The rubber compounds which were employed `are those conventionally usedin textile print blanket manufacture, and considerable variability inthe choice of suitable compounds exists. Thus, it is possible to usecompounds which lie within the production experience or compoundingpreference of an experienced textile blanket manufacturer. Therubber-coated plies may be cold pressed to ensure the adhesion of therubber to the adjacent layer or the rubber-compound may be `of thepressure-sensitive type to obviate such cold pressing.

The word rubber has been used in a generic sense and implies no chemicalsignificance whatever. It signifies only long-chain, vulcanizablepolymeric substances of whatever chemical origin which possess therequisite physical properties of exibility, resilience, :or resistanceto the colors and solvents used in the screen printing process.

Although this blanket has been designed specifically for solvingproblems arising in the screen printing industry, the usefulness of sucha blanket is not confined to screen printing machinery. Presses exist inwhich the work is carried by a blanket linearly under a rotatingprinting surface. Other presses exist where the printing surface isattached to the blanket itself land passes under a cylinder whichcarries the sheet to be printed. On both such presses, these blanketswill find utility and maintain page dimensions in a superior manner.

What is claimed is:

1. The process of manufacturing a blanket suitable for use on `a screenprinting machine which consists of coating one side of a length oftextile with a rubber compound, looping the textile length loverpulleys, splicing its ends together to form an endless loop to formthereby a cylinder ply, running in the yply by vapplying power to apulley to rotate the said ply, meanwhile applying tension to the ply inincremental amounts until the applied tension reaches about 10 poundsper inch of width, continuing the running-in until no slack developsfurther and the ply maintains a constant length, thereafter, whilemaintaining the said tension, superposng a layer of essentiallynon-stretchable rubber-coated cord on said coated ply by winding saidcord in a helix about said ply while maintaining the tension applied tothe cord at a value not exceeding 2 pounds, covering the cord layer withat least a second named rubber-coated textile ply while the saidcord-covered structure is maintained under tension and then vulcanizingthe Aassembly between suitably finished platens under heat and pressureto produce thereby a consolidated, unitary blanket structure, having asmooth working surface.

2. The process of claim 1 wherein a third-named ply of fabric havingboth surfaces coated with rubber compound is superposed on the saidsecond-named coated ply and the blanket is thereafter cured under heatand pressure to produce a unitary blanket structure.

3. The process of claim 1 wherein `a third-named ply of fabric, coatedon its lower side only with a rubber compound, is superposed on the saidsecond-named ply, and the blanket thereafter is cured under heat andpressure to produce a unitary blanket having a working surfacecomprising exposed fabric.

4. The process of claim 1 wherein Cords are simultaneously wound on saidply as two helices, each begin ning adjacent the center line of said plyand extending outwardly respectively to the rightand left-hand marginsof said ply.

5. The process of claim 1 wherein the said cords consist of glass, andthe said cords are helically wound over the said cylinder ply whilesubject to a tension of approximately one pound.

6. The process of claim 5 wherein, subsequent to the application of saidglass cord winding, the cord-covered cylinder ply is stretched betweenrollers at a tension of between 20 and 40 pounds per transverse inch.

7. The process of claim 6 wherein the said tension is maintained at 25pounds per transverse inch.

8. A blanket adapted for use 4on roll drive screen printing machineryand capable of maintaining the deviation of repeat pattern register towithin 1.015 inch per blanket revolution which consists of arubber-coated cylinder ply rendered dimensionally stable by running-inand stretching under a tension of about 10 pounds per transverse inch, ahelix of rubber-coated cord wound about the exposed surface of saidcylinder ply at a cord tension not in excess of 2 pounds and extendingacross the said surface, and at least a second coated ply covering saidhelical layer of cords, the said blanket having been cured under heatand pressure to produce a unitary blanket structure presenting a smoothworking surface.

9. A blanket as claimed in claim 8 wherein the helix of rubber-coveredcord is composed of glass cord wound on said cylinder ply under tensionapplied to the cord not exceeding l pound, the said cords being free ofcrimping within the blanket structure when passing around the blanketdriving rolls.

References Cited UNITED STATES PATENTS 228,186 1/1880 Gandy 156-229 X1,096,896 5/1914 Ellis 161-400 X 1,412,309 4/1922 Lambert 156-172 X2,386,761 10/ 1945 Wetherbee. 2,489,791 1 1/ 1949 Liles et al. 2,547,2204/1951 Merrill. 2,630,603 3/1953 Freedlander et al. 156-137 X 3,122,934-3/1964 Fike. 2,653,886 9/ 1953 Gentle.

ROBERT F. BURNETT, Primary Examiner.

I) W. POWELL, Assistant Examiner.

U.S. C1. X.R.

8. A BLANKET ADAPTED FOR USE ON ROLL DRIVE SCREEN PRINTING MACHINERY ANDCAPABLE OF MAINTAINING THE DEVIATION OF REPEAT PATTERN REGISTER TOWITHIN $.015 INCH PER BLANKET REVOLUTION WHICH CONSISTS OF ARUBBER-COATED CYLINDER PLY RENDERED DIMENSIONALLY STABLE BY RUNNING-INAND STRETCHING UNDER A TENSION ABOUT 10 POUNDS PER TRANSVERSE INCH, AHELIX OF RUBBER-COATED CORD WOUND ABOUT THE EXPOSED SURFACE OF SAIDCYLINDER PLY AT A CORD TENSION NOT IN EXCESS OF 2 POUNDS AND EXTENDINGACROSS THE SAID SURFACE, AND AT LEAST A SECOND COATED PLY COVERING SAIDHELICAL LAYER OF CORDS, THE SAID BLANKET HAVING BEEN CURED UNDER HEATAND PRESSURE TO PRODUCE A UNITARY BLANKET STRUCTURE PRESENTING A SMOOTHWORKING SURFACE.